This invention generally relates to electronic systems and in particular it relates to an improved switched capacitor integrator circuit.
For low power, it is desirable to share the input and reference capacitors in a switched-capacitor integrator. Unfortunately, this means that the circuit driving the integrator input must discharge this capacitor of the reference charge left over from the previous cycle, then charge it with the input signal. This requires higher bandwidth and power from the driver.
For low power, it is desirable to share a single switched capacitor at the input of an integrator for both the signal input and the reference capacitor. This reduces the total input capacitance by a factor of 4 (for the same KT/C noise) and greatly reduces the load, which the integrator""s opamp must drive, thereby allowing it to use less power. Unfortunately, this capacitor sharing causes a few problems. One is the fact that the circuit which drives the input to the integrator must not only charge the input capacitor with signal charge, it must also discharge this capacitor of the charge left on the capacitor from the reference feedback of the previous half-cycle. Normally this would require a high-bandwidth (high power) driving circuit to charge this capacitor.
A switched capacitor integrator that shares a switched capacitor at the input of the integrator for the signal input and the reference capacitor. The operation of the circuit includes discharging the capacitor with a first clock signal; transferring an input voltage onto the capacitor with a second clock signal; applying a reference voltage to a first end of the capacitor with a third clock signal; and coupling a second end of the capacitor to the integrator with the third clock signal while the reference voltage is applied to the first end of the capacitor.